Thèse de doctorat : Sciences de l'éducation : Lille 1 : 2003 ; 3297 E. / Thèse : 2003LIL12005. Résumé en français. Bibliogr. p. 260-269.

Thesis (M.U.D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaves 100-104).

No description available.

This thesis investigates how changes in population size and spatial movements of individuals have shaped the distribution and abundance of neutral genetic variation in the arctic fox. This is done through mitochondrial and microsatellite DNA analyses on samples covering most of the species’ distribution, but with special emphasis on Scandinavia. On the species level, nucleotide diversity was relatively low, which indicated a historical expansion in population size in connection with the onset of the last Ice Age. It is thus possible that the glacial cycles have affected the arctic fox, and other cold-adapted species, in a way opposite to their effect on temperate species. Gene flow seemed to be high among arctic fox populations on a circumpolar scale, especially between populations where lemmings are the main food source, which could be explained by the spatial synchrony in lemming fluctuations. In Scandinavia, the arctic fox went through a severe demographic bottleneck in the beginning of the 20th century. Although some genetic variation was lost during this bottleneck, the loss was much smaller than expected, probably due to post-bottleneck gene flow from Russia. The arctic fox in Scandinavia is divided into four relatively isolated populations. Within each population, dispersal seemed to be high despite the high availability of empty territories close to natal dens, which supported the hypothesis that lemming fluctuations influence arctic fox dispersal. Genetic analyses on samples collected between 1989 and 2004 indicated an ongoing genetic drift and inbreeding within the Scandinavian populations. Furthermore, individual genetic variation was negatively associated with fitness, which could be attributed to an ongoing inbreeding depression. Analyses on faecal samples suggested that arctic foxes move higher up in the mountains and farther from the tree-line during summer compared to winter. This seasonal shift in distribution is probably caused by interspecific competition from the red fox, which is likely to be higher during summer due to red fox predation on arctic fox cubs. The results presented in this thesis have several implications for the conservation of the Scandinavian arctic fox. The finding of four isolated populations within Scandinavia and an ongoing inbreeding depression suggests that the risk of extinction is higher than previously thought. Conservation actions need to be taken in all populations to be effective, and could include genetic restoration through translocation.

The spatial scale at which populations are genetically structured is of immense interest for the understanding of a species’ ecology and evolutionary biology. This can have important implications for management of resources as well as predicting responses to future change. Rainbow smelt (Osmerus mordax) is an anadromous species with a relatively short freshwater residence time compared to other species with similar life-history strategies. Therefore, while they offer the opportunity to sample distinct spawning aggregations, they also offer an insight into the relative roles of contemporary and historical factors shaping connectivity among marine populations, an area of great interest, and for which further understanding is required. With the use of both mitochondrial DNA and nuclear microsatellite markers, I explored the historical and contemporary factors influencing population structure in smelt. While previous phylogeographic work on this species has resolved two mtDNA lineages dating back to previous glacial episodes, I document the discovery of a zone of contact between these lineages in Newfoundland. This is in addition to the established contact zone in the St. Lawrence estuary, and results in a longitudinal distribution of the races with one race predominating on opposite ends of the species distribution, while the other race is geographically intermediate. Patterns of nuclear genetic variation largely mirror the phylogeographic signals in Newfoundland and suggest a more recent colonization of the Avalon Peninsula as well as implicating a remnant historical signal of colonization of the west coast of Newfoundland from the mainland. In addition, contrasting patterns of genetic diversity and levels of differentiation were apparent between the mainland and Newfoundland and suggest differing scales of dispersal within this species. While the population structure within Newfoundland is most consistent with dispersal restricted to within bays, larger scale biogeographic regions were identified in the mainland range, suggesting dispersal is more common and widespread. In addition, sampling of different run times (i.e. ‘early’ vs. ‘late’) demonstrated the potential for isolation by time when spawning events are separated by a break in activity. Overall, these results shed light into the possible roles of both historical and contemporary factors shaping the dynamics and connectivity among populations.

No description available.

This study examines the quantitative aspects of the demographic characteristics of the Indian population of South Africa over a period of one-hundred-and-thirty years, from 1860 to 1991, within the framework of demographic transition theory. It informs us about a distinctive group of people within a country of mixed races and presents a hitherto uncollated historical account of the demographic changes of a small, specific, minority group, in a racially mixed society, within a developing country. Its emphasis lies in tracing the historical evolution and development of a demographically unbalanced population to one that today may be regarded as falling within the general demographic classification of an 'ageing' population. It is set within the framework of demographic transition theory and a discussion of the formation of this theory and its usefulness today is included in this work. Changes in the vital rates of mortality and fertility are examined in detail and an in-depth look is taken at changes in the age and sex structure over time. Apart from a detailed account of the patterns and numbers of indenture during the years 1860 to 1911, the core of the analysis is contained in three major chapters dealing with population structure, mortality and fertility. The bulk of the primary data was obtained from the results of twelve censuses between 1891 and 1991, inclusive. During the relatively short time-span of Indian settlement in South Africa, considerable demographic changes have taken place in this population. This study traces the progression of the population far beyond its original, unbalanced structure, which arose from the practice of indentured labour. After this practice was abandoned, growth and structural change took place almost entirely by natural increase, the balance of births and deaths. The population passed through the youthful, expanding stage of development to a structure that today resembles, in many ways, those to be found in most developed, industrialised countries of the world - with a slow rate of growth, a decreasing proportion of children under 15 years of age and an increasing proportion aged 60+ years. The social and economic challenges which face the Indian community today are very different from those encountered in the previous 130 years of settlement in this country and can be directly related to the extensive demographic changes that have occurred over this period. These demographic changes and their occurrence over time form the essence of this treatise. / Thesis (Ph.D.)-University of Natal,Durban, 2002.

Much research was performed in order to find alternative energy sources. In the new concept presented in this thesis, methane was produced by a microbial consortium which is fed only by glycolate excreted by photosynthetic algae. It was unknown how the biogas production and the process stability are influenced by certain parameter shifts in glycolate feed, pH of the feed, oxygen input and temperature. Therefore, different parameter changes were applied to the reactor system. Gas formation and composition, pH, FosTac and organic acid content in the media were analyzed. Additionally, the community composition induced by the changes of the process parameters was analyzed. Therefore, the single cell level using flow cytometry and the genetic level using T-RFLP were observed. The R based tool flowCyBar was applied to follow community dynamics and to find key players in the process. Abiotic and biotic parameters were used for correlation analysis (Spearman´s Rho) to determine specific functions of sub-communities and the T-RFs found in the whole community. The cultivation at room temperature indicated that the biogas yield was 30 % lower in comparison to the cultivation at 37°C. The community seemed to be able to sustain pulsating oxygen input in case glycolate as substrate is available. Additionally, the system was able to recover after the oxygen application of one day. A linear correlation between the feed glycolate and the biogas production was observed (R^2 = 0.97). High biogas yields were obtained (up to 90 %) indicating that glycolate is a suitable substrate. The efficiency of the process was high with 41 ± 3 % methane in the biogas under defined conditions. It could be observed that biogas can be produced on glycolate as mono-substrate by a complex microbial community while it remained complex over the complete study (505 days cultivation) although glycolate was used as sole carbon source. Key sub-communities (e.g. cluster 1 and 3) and T-RFs (e.g. T-RF representing Planctomycetaceae or 67 bp) were defined and indicated the status of the bioreactor. The community was able to sustain certain parameter shifts, like changes in the pH of the feed (from 3 to 7), while others led to a complete crash of the system, like high glycolate feeds (3.6 g d^-1 L^-1). All in all, the stability of the process seemed to be susceptible on external influences.

Near the beginning of the last century, R. A. Fisher and Sewall Wright devised an elegant, mathematically tractable model of gene reproduction and replacement that laid the foundation for contemporary population genetics. The Wright-Fisher model and its extensions have given biologists powerful tools of statistical inference that enabled the quantification of genetic drift and selection. Given the utility of these tools, we often forget that their model - for reasons of mathematical tractability - makes assumptions that are violated in many real-world populations. In particular, the classical models assume fixed population sizes, held constant by (unspecified) sampling mechanisms. Here, we consider an alternative framework that merges Moran’s continuous time Markov chain model of allele frequencies in haploid populations of fixed size with the density dependent models of ecological competition of Lotka, Volterra, Gause, and Kolmogorov. This allows for haploid populations of stochastically varying – but bounded – size. Populations are kept finite by resource limitation. We show the existence of limits that naturally generalize the weak and strong selection regimes of classical population genetics, which allow the calculation of fixation times and probabilities, as well as the long-term stationary allele frequency distribution.

Human food production activities can dominate natural systems, altering ecological and evolutionary aspects of the environment. Disease-mediated interactions are of particular concern. For example, parasites may "spill-over'' from farms to wildlife. Parasites isolated on farms can evolve resistance to treatment chemicals , but "spill-back'' from wildlife to farms may alter evolutionary dynamics. Here, we consider exchange of parasites (Lepeophtheirus salmonis) between wild (Oncorhynchus gorbuscha) and farmed salmon. We derive and analyze discrete-time models that implicitly include wild salmon migrations. First, we extend a standard fisheries model to show parasite exchange affects "line-dominance'' in the population ecology of salmon. Second, we extend a classic population genetics model to show that wild salmon can theoretically provide an "ecosystem service'' by delaying the onset of chemical resistance in parasites on farms. This service, however is affected by a nonlinear feedback if farm parasites spill-back to affect wild salmon. / Applied Mathematics